Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $49.29   6.701%   $52.5929   $52.59   $52.60   $52.60  
  Purchase #2 $247.57   3.432%   $256.0666   $256.07   $256.05   $256.10  
  Purchase #3 $72.65   7.468%   $78.0755   $78.08   $78.10   $78.10  
  Purchase #4 $124.93   7.874%   $134.767   $134.77   $134.75   $134.80  
  Purchase #5 $190.58   8.165%   $206.1409   $206.14   $206.15   $206.10  
  Purchase #6 $201.63   3.119%   $207.9188   $207.92   $207.90   $207.90  
  Purchase #7 $241.70   3.259%   $249.577   $249.58   $249.60   $249.60  
  7 purchase totals = $1,128.35       $1,185.1387   $1,185.15   $1,185.15   $1,185.20